The classifier is working pretty well, and has the potential to be more convenient that maintaining procedural rules like Outlook's Rules or procmail on UNIX in years past. More convenient than Google Inboxes bundles, because at least other email clients can access IMAP folders (although most have really, really, bad UIs for accessing folders).

It is, however, a maintain the mapping of buckets to folders.

Here's an idea to simplify that:

Let all subfolders of Inbox be, implicitly, buckets.

e.g. INOX/low-priority corresponds to a bucket "low-priority". And so on.

This would make it easy to create new buckets, and to rename and delete old buckets.

The cost: POPFile would need to periodically scan for new IMAP folders. More likely, scan all IMAP folders, looking for new ones. (Pity IMAP does not have notifications for events like new, delete, rename folders).